Lamp basing method



1968 H. H. HOMER ETAL 3,361,393

' LAMP BASING METHOD Filed Aug. 18, 1964 SAMUEL BO RACE H. H ER STATION B ILIP E LYNN INVENTOR 8 'BY .d M

ATTORNEY United States Patent Oilice 3,361,893 LAMP BASING METHOD Horace H. Homer, Arlington, and Philip F. Lynn, Lynnfield, Mass., and Samuel Boyd, Newton, N.H., assignors to Sylvania Electric Products, Inc., a corporation of Delaware Filed Aug. 18, 1964, cr. No. 390,3?6 2 Claims. (Cl. 219-137) This invention relates to the manufacture of electric lamps and the like, and more particularly to the welding of the side lead-in wire of an incandescent lamp to the metal base with which the lamp is provided.

In the manufacture of incandescent electric lamps, a pair of lead-in wires extending from an end of the glass lamp envelope are mechanically and electrically connected to the metal base with which the lamp is provided. One of these lead-in wires extending from an end of the glass lamp envelope is mechanically and electrically connected to an eyelet-type electrical contact, set in a disc of insulating material in the bottom of a metal shell, to define a bottom contact. The other lead-in wire is shaped and positioned so that it overlies the lip of the metal shell and extends outwardly therefrom adjacent to the glass lamp envelope, and is joined to the shell to define a side contact.

Over the years various techniques have been employed to effect the desired electrical and mechanical connection of these lead-in wires to the lamp base by soldering, welding or a combination thereof, i.e., soldering one contact and welding the other. The bottom contact has never presented any significant problem of long duration. However, such is not the case with respect to the side contact.

One of the more significant problems associated with welding the side contact is shaping and positioning the wire with respect to the lip of the base shell so that a good electrical and mechanical connection can be assured, and at the same time protect the glass lamp envelope from the heat generated and molten metal formed during the welding operation.

Generally speaking, the work is prepared for the side wire welding operation by shaping and positioning the side lead-in wire so that it overlies the lip of the base shell and the free end thereof extends outwardly from a point between the lip of the base shell and the lamp envelope. An electrode is then advanced toward the free end of the wire and a DC are is struck therebetween. The high current density in the arc melts the wire and a balling of the free end of the wire occurs. This mass of molten metal maintained in the molten state by the arc partially melts the adjacent portion of the base shell and causes an inter-diffusion of the two metals therewith to define a side wire weld.

Some rather chronic conditions have long been associated with this operation. One of these conditions is the tendency of the mass of molten metal to run over the lip of the base shell onto the glass lamp envelope. This is both an appearance defect and a potential source of glass failure. In order to minimize this condition, the wire shape and length must be accurately controlled within very close tolerances. In addition, it has been found that some relief can be obtained if a gap not greater than three-thousandths of an inch is established between the wire and the lip of the base shell. These chronic conditions are further aggravated when brass rather than aluminum bases are used. Although these conditions can be alleviated somewhat by the installation of certain controls insofar as laboratory and pilot production runs are concerned, they do not readily lend themselves for adaptation to high speed automatic lamp manufacturing equipment as a practical matter because the tolerances are too critical to maintain consistently.

3,361,893 Patented Jan. 2, 1968 In view of the foregoing, a principal object of this in vention is to provide a new technique for welding the side lead-in wire to the base shell of an incandescent lamp.

This and other objects, advantages and features of this invention are attained, in accordance with the principles of this invention, by positively positioning the wire against the lip of the base shell during the welding cycle. Although any one of several mechanical devices to obtain this positive contact are possible, a major problem is encountered in the selection of the material with which the work is to be contacted and to which a force is applied sufiiceint to insure the positive positioning of the wire against the lip of the base shell.

Obviously, the pressure pad must be of a material which is non-conductive of electricity, mechanically strong enough not to deform after repeated applications of the required pressure and capable of withstanding the exceedingly high temperature of the arc. Several different materials, such as glass, quartz, transite, soapstone and lava for example were tried but all were found deficient in one respect or another. With the exception of soapstone, all the materials tried acquired a metallic coating sputtered from the are. This caused a short circuiting of the arc and no weld occurred. Although the soapstone did not coat with the metal, it was too soft to stand up under repeated pressure.

In an effort to resolve this problem, we have discovered that if a thin film of Water were applied to the pressure pad prior to initiation of the welding cycle, this will prevent the metallic buildup. Initial evaluation of this technique would suggest that the film of water would make the pressure pad conductive, as did the metal layer. However, such was found not to be the case. Although a thin black deposit does form on the pressure pad member, it does not adversely affect striking of an arc. Without the film of water, thick deposits of shiny copper build up rapidly.

In the specific embodiment of the invention illustrated in the accompanying drawing:

FIGURE 1 is a fragmentary elevational View showing a pressure pad assembly and its disposition in the path of the work, a lamp assembly being shown in phantom.

FIGURE 2 is a fragmentary elevational view similar to FIGURE 1, except that a lamp assembly is shown in welding position with respect to the pressure pad assembly.

FIGURE 3 is a fragmentary detail on an enlarged scale of the weld locus showing particularly the relative locations of the lamp envelope, the base shell, the pressure pad and the electrode.

FIGURE 4 is a schematic plan view of a segment of the path traversed by the work, a lamp envelope and a base being shown in phantom at the station immediately preceding and the station immediately following the welding station.

In the specific embodiment of the invention illustrated in the accompanying drawing, a pressure pad assembly comprises a spring-loaded lava wheel 10 pivotally mounted for rotational movement at 12 and a wick 14 for dispensing water onto the wheel 10. The spring-loaded wheel 10 normally lies in the path of the work which is shown in phantom in FIGURE 1 and at Station A in FIGURE 4. Thus, when a conveyor having a plurality of heads thereon for carrying the work to a plurality of stations, including Stations A, B and C as shown in FIGURE 4, advances the work from Station A as shown in FIGS. 1 and 4 to Station B, the welding station as shown in FIGS. 2, 3, and 4, the wheel 10 is displaced from the path of the work in the direction of the arrow in FIG. 2. As the work moves into Station B, the wheel 10 is also caused to rotate because of the tangential force applied thereto by the advancing work. Thus, the advancing bulb 11, with a base 13 mounted thereon, displaces the wheel 10 downwardly and causes it to rotate. As shown on an enlarged scale in FIG. 3, the circumferential edge of the wheel 10 assumes a position wherein it is applying a positive force on the side lead-in wire 15 against the lip 17 of the shell 19 of the base 13.

This is the disposition of the work and the pressure pad assembly at Station B, the welding station, as shown in FIGS. 2, 3, and 4. An RF discharge is then initiated between electrode 16 and the projecting side lead-in wire 15 followed by the DC are to effect a welding of the wire 15 to the shell 19 of the base 13. This completes the welding operation, the completed work advances to Station C as shown in phantom in FIG. 4 and a new article of work is advanced to Station B for the Welding operation.

From the foregoing description of an operating cycle of the method of this invention, it will be appreciated that the wheel 10 is caused to rotate by an article of work as that article moves out of the welding station as well as when that same article moves into the welding station. This insures the presentation of a different segment of the wheel 19 to each lead-in wire to be welded. It also permits the use of a stationary wick 14 since this intermittent rotational movement of the wheel 10 will continually present a new segment of the wheel to be wetted. This new welding method also makes possible the use of a stationary electrode, thus eliminating the need for a relatively complicated arrangement to provide proper tolerances for electrode travel.

In addition, the criticalness of the wire shape is greatly reduced and the need for the use of an inert gas during the welding operation has been eliminated.

What we claim is:

1. The method of welding the side lead-in wire of an electric lamp to the base thereof, said method comprising: positioning the side lead-in wire so that its free end projects from between the rim of the base shell and the lamp bulb; interposing a wetted pressure pad between said projecting free end of said lead-in wire and said lamp bulb whereby a positive force is applied to said lead-in wire against said rim of said base shell; and striking an are between an electrode and said projecting lead-in wire, while said lead-in wire is constrained as aforesaid, whereby said lead-in wire is welded to said base shell.

2. In the manufacture of electric lamps wherein lamp bulbs, each having a base disposed on one end thereof and a lead-in wire projecting from between the rim of the base shell and the lamp bulb, are advanced through a path to a plurality of work stations including a welding station, the combination of a substantially circular, a freely rotatable pressure pad located at said welding station, a peripheral edge of said pressure pad normally lying in said path through which said lamp bulbs are advanced whereby each advancing lamp bulb displaces said pressure pad out of said path and effects rotation thereof, a segment of the peripheral edge of said pad being interposed betwen said projecting lead-in wire and said lamp bulb at said welding station whereby a positive force is applied to said lead-in wire against said rim of said base shell to thereby postively position said lead-in wire for the welding operaton; and means, disposed at said welding station, for wetting said pressure pad.

References Cited UNITED STATES PATENTS 5/1955 Albrecht 2l9137 10/1957 Albrecht 2l9l30 

1. THE METHOD OF WELDING THE SIDE LEAD-IN WIRE OF AN ELECTRIC LAMP TO THE BASE THEREOF, SAID METHOD COMPRISING: POSITIONING THE SIDE LEAD-IN WIRE SO THAT ITS FREE END PROJECTS FROM BETWEEN THE RIM OF THE BASE SHELL AND THE LAMP BULB; INTERPOSING A WETTED PRESSURE PAD BETWEEN SAID PROJECTING FREE END OF SAID LEAD-IN WIRE AND SAID LAMP BULB WHEREBY A POSITIVE FORCE IS APPLIED TO SAID LEAD-IN WIRE AGAINST SAID RIM OF SAID BASE SHELL; AND STRIKING AN ARC BETWEEN AN ELECTRODE AND SAID PROJECTING LEAD-IN WIRE, WHILE SAID LEAD-IN WIRE IS CONSTRAINED AS AFORESAID, WHEREBY SAID LEAD-IN WIRE IS WELDED TO SAID BASE SHELL. 